1. Field of the Invention
The present invention relates in general to force-sensitive transducers and in particular to a load sensor for measuring the tension level on cylindrical rods used as tie rods in a die-casting or other machine.
2. Description of the Prior Art
The ability to measure force or load is a vital part of many industrial processes. Recognizing that a structure undergoes dimensional changes when subjected to a load, a measure of the dimensional change in a structure can accurately indicate the amount of force applied thereto. Such measurement is usually made through the use of a wire, foil, or semiconductor element intimately bonded to the structure. By measuring the change in the electrical resistance of the element, which resistance is a function of the change in cross section of the element due to alterations in the dimensions of a structure, it is possible to accurately measure the load applied to the structure.
Many transducer devices have been developed for attachment to structures for measuring the amount of stress applied thereto. U.S. Pat. No. 3,210,993 to Shoor et al. discloses an electro-mechanical transducer including a cylindrical force sensing element and a plurality of bolts which are utilized to pre-load the force sensing element. U.S. Pat. No. 3,388,590 to Dryden discloses a strain sensing transducer attached to the connector pin positioned within a female connector receptacle. The strain produced by the pin biasing means in the wall of the receptacle is sensed by the transducer and the resulting electrical signal produced is a measure of the quality of the electrical connection between the pin and the receptacle.
U.S. Pat. No. 3,389,459 to Russell discloses a strain gauge ring for a pressure transducer. The strain gauge is installed in a groove cut in the surface of a force ring and the ring is mechanically deformed adjacent the gauge to elongate the gauge and lock the same within the groove. A ball is used in a countersink to concentrate the load at one end of the sensor. A retainer ring can be utilized to pre-load the sensor. U.S. Pat. No. 3,742,757 to Callahan discloses a load cell for measuring stresses in pre-stressed concrete. Stress forces are applied to opposite sides of the cell, whereby a deflection of a pre-stressed internal member is proportional to the applied stress. Any changes are detected by variations in the output of the strain gauges attached to the internal member.